Four hospitals in Central Massachusetts received an A for safety in twice-a-year reviews by a national group on Monday. The Leapfrog Group s fall reviews include As for Harrington Hospital in Southbridge, Heywood Hospital in Gardner, Marlborough Hospital and Milford Regional Medical Center. Among the area s largest hospitals, Saint Vincent Hospital got a B and UMass Memorial Medical Center s Memorial and University campuses in Worcester both earned a C. The Leapfrog Group scores more than 2,600 hospitals on a grade rank of patient safety based on publicly available data on prevention of medical errors, infections and other potential harms on patients. Of 58 hospitals rated across Massachusetts, 33 received As, 14 got Bs, and 11 got Cs.